Due to a remarkable growth of portable systems, the demand for low-cost but high performance temperature sensors is on an increasing trend. The important applications of temperature sensors includes the following, but not limited to, (a) power consumption control in integrated chips that includes a processing unit; (b) thermal compensation in application specific integrated circuits; (c) local temperature monitoring in fabrication factories; and (d) temperature control in automobiles and consumer electronic devices.
In addition to low cost and high performance, the power consumption of temperature sensors should be as low as possible to be applicable to the battery-powered portable systems. Furthermore, with low power consumption, the error caused by self-heating will be reduced and the power consumption of the integrated chips will not be significantly increased.
A heat map of an integrated chip illustrates the heat generated and the corresponding temperature in different parts of the integrated chip. Generally, the area around a processing unit or logic unit is the hottest region or hot spot. In a typical integrated chip, there are multiple hot spots. However, owing to a large area of existing temperature sensors, they are placed quiet far away from the hot spot(s). This results in a temperature gradient which can be as high as +/−15° C.
In addition, the temperature gradient is not constant, which further degrades the performance of the existing temperature sensors since a maximum temperature threshold is required to be kept low to account for the temperature gradient. The variation in the temperature gradient may be caused by local hot spots within the processing unit.
Thus, a number of temperature sensors that can be used on the integrated chip are limited because of the large size of the existing temperature sensors. Also, efficient thermal management on the integrated chip is not possible because of the degraded performance of the existing temperature sensors.
The existing temperature sensors also suffer from noise isolation and high process spread. In addition, there are very strict requirements on reference voltage levels and reference current levels. A poor correlation exists between individual temperature sensors which makes it difficult to use multiple temperature sensors on the integrated chips.
The commonly used existing temperature sensor includes time-to-digital converter based CMOS sensors and CMOS gate leakage based sensors. These CMOS sensors have poor linearity and high process spread. In addition, the CMOS sensors are supply sensitive and also susceptible to noise.